1. Field of the invention
The present invention pertains to a float system for detecting leaks in storage tanks and, in particular, a float system minimizing the effects of surface tension for detecting leaks in underground tanks that store hydrocarbon products with high precision.
2. Statement of the Problem
In U.S. Pat. No. 4,850,223 the inventor set forth a novel system for detecting, collecting and processing data regarding the leakage rate of underground storage tanks. As set forth in this patent, it is necessary that the leak detection apparatus for an underground storage tank be extremely sensitive so that it can detect leaks in the range of 0.02 gallons per hour or less. The sensitivity of this measurement becomes further complicated since it is extremely difficult to detect the loss (or gain) of 0.02 gallons of fluid per hour in an underground storage tank capable of storing 10,000 gallons or more such as is commonly found in gas stations. For example, in a nine foot diameter tank twenty-one feet long which is half full, the removal of one gallon of gasoline lowers the fluid level 0.00629 inches. The loss of 0.02 gallons per hour would cause a fluid level drop of 0.0001257 inches or 125.7 micro inches per hour. It is difficult to measure changes in fluid level of this magnitude due to the cross-sectional area of the surface being about 27,000 square inches. At 95 percent full, which is the ideal level for testing tanks volumetrically, the cross-sectional area is still very large being about 16,000 square inches. In order to measure accurately such a change in fluid level, various factors such as temperature, vibration, etc. must be taken into account or, hopefully, minimized. A need exists to increase the sensitivity of this leak detection by about 100 percent to a level capability of 50 microinches.
A problem exists with respect to the interaction between the float and the fluid. In U.S. Pat. No. 4,850,223, an elongated cylindrical float was utilized. Three wheels were attached to the upper end of the float and three wheels were attached to the lower end of the float so as to allow the float to ride within a tubular probe. A need exists to eliminate the use of wheels which contact the interior of the tubular probe and, furthermore, a need exists to minimize or significantly reduce the effect of surface tension between the fluid and the float. The overall problem to be satisfied, therefore, is to provide a float that provides greater precision in detecting the true level of the fluid in the tank.
A need exists to provide a float design which floats within the tube without touching the tube and one that inherently minimizes the surface tension between the float and the fluid. Furthermore, a need exists to insure that the float will always be in its true buoyancy position based upon the specific gravities of the float and the fluid without any change in the true buoyancy position due to surface tension. The effect of surface tension becomes more important when the level of fuel changes. The dropping (or rising) of fuel due to a leak in the tank may actually not be detected in the short time interval due to the float maintaining its position due to residual surface tension or due to the float reorienting into an exaggerated position also due to surface tension. Hence, a need exists to insure that the float will always assume a true buoyancy position with respect to surface tension and the level of the fluid before obtaining a level reading.
3. Solution to the Problem
The present invention provides a solution to the above problem and directly satisfies each of the needs set forth with respect to the problem. First, the float is designed to float within the tube without touching the inner surfaces of the tube. Second, the float of the present invention utilizes a geometric design having a plurality of different tapered surfaces to minimize and to substantially reduce the effects of surface tension between the float and the fluid. Finally, the float of the present invention is vibrated just before a level reading is obtained in order to allow the float to assume the true buoyancy position with respect to the fluid before a level reading is obtained.